The Evolution of Functionally Redundant Species; Evidence from Beetles

Abstract

While species fulfill many different roles in ecosystems, it has been suggested that numerous species might actually share the same function in a near neutral way. So-far, however, it is unclear whether such functional redundancy really exists. We scrutinize this question using extensive data on the world’s 4168 species of diving beetles. We show that across the globe these animals have evolved towards a small number of regularly-spaced body sizes, and that locally co-existing species are either very similar in size or differ by at least 35%. Surprisingly, intermediate size differences (10–20%) are rare. As body-size strongly reflects functional aspects such as the food that these generalist predators can eat, these beetles thus form relatively distinct groups of functional look-a-likes. The striking global regularity of these patterns support the idea that a self-organizing process drives such species-rich groups to self-organize evolutionary into clusters where functional redundancy ensures resilience through an insurance effect.

From Hutchinsonian ratios to spatial scaling theory: the interplay among limiting similarity, body size and landscape structure

“…Indeed, this is the pattern herein reported for carnivorous and herbivorous coleopterans on both observed trends and deviations from null model expectations (Fig. In addition, the observed relationship between similarity and body size indicates that a focus on average similarity, as community wide size ratios, may not be the best approach for the analysis of size ratios (Losos et al 1989, Dayan and Simberloff 2005, Scheffer et al 2015. These patterns provide support for long-standing theoretical predictions that have not accumulated as much evidence as their central role in ecological theory may demand (Ritchie 2010, Marquet et al 2014).…”

“…Thus, temporary ponds are proper model systems because several local communities are available, have clear limits and encompass large gradients in physical structure (Arim et al 2011). The range of body sizes covered by these species allows for the detection of the role of size-dependent mechanisms in community assembly (Scheffer andvan Nes 2006, Borthagaray et al 2012). For example, the bottom topography of ponds and the spatial filling of ponds determine gradients in the landscape fractal dimension that can be related to community structure.…”

“…Aquatic coleopterans inhabiting ponds have also been a classical model in ecology (Hutchinson 1959). The range of body sizes covered by these species allows for the detection of the role of size-dependent mechanisms in community assembly (Scheffer andvan Nes 2006, Borthagaray et al 2012).…”

Cryptic species as a window into the paradigm shift of the species concept

“…Cryptic species having a roughly similar role in the ecosystem (Eltonian niche) but differing in their environmental requirements and responses to various stressors may be functionally redundant. If so, cryptic species may be critically important in stabilizing ecosystem functioning (Elmqvist et al, 2003;Harvey, Gounand, Ward, & Altermatt, 2017;Scheffer et al, 2015). To our knowledge, a single study using cryptic nematodes as a model system explored differences in the functional role of cryptic species (De Meester, Gingold, Rigaux, Derycke, & Moens, 2016).…”

The distribution and role of functional abundance in cross‐scale resilience

“…compartmentalization by size has been demonstrated by several ecological theories (Vergnon et al 2012, Rudolf and Rasmussen 2013, Scheffer et al 2015, but they do not explain how abundance among species will be distributed within a functional group or at specific scales. Both phylogeny and broader abiotic factors constrain the number of scale domains at which a functional group can occur.…”